1. Field of the Invention
The present invention relates to a fuel injection system for an internal combustion engine for automobiles, for example. More particularly, the present invention relates to a fuel injection system for an internal combustion engine, which is equipped with fuel atomizing device such as an air feed pump or a multi-port injector for atomizing the fuel, as injected by an injector, by using a part of the output of the engine.
2. Related Art
For the reduction of the unburned HC in exhaust gases and stabilizing the combustion, there have been hitherto embodied a variety of techniques for atomizing the fuel injected by a fuel injector. There is a technique in which a difference in the pressure between the upstream and downstream sides of a throttle valve is utilized to bring intake air due to the differential pressure into impingement against the fuel injected from the injection port of the injector thereby to atomize the fuel. This technique is generally known as the differential pressure type air-assisted type injector. This injector establishes a mean gas particle size of about 80 to 100 microns.
In recent years, however, there has been a demand for reducing the gas particle diameter to a smaller size. In order to satisfy this demand, there has been proposed a technique in which an air feed pump is driven by a driving source such as the motor output of a battery or the output of a crankshaft to atomize the fuel with the pressurized air fed from the pump. According to this air-assisted type injector, it is possible to provide a fuel gas particle diameter of about several tens microns.
In the air-assisted type injector using the air feed pump, however, the electric power of the battery is consumed by the motor drive, for example, causing a problem that the battery voltage unexpectedly drops. In this case, the power generation load on the internal combustion engine increases to require a battery of large capacity for avoiding the problem. When the crankshaft output is employed as the drive source, on the other hand, the engine output is partially consumed for the air-assisted type so that the energy loss occurs, causing an unexpected output drop. In this case, the load on the internal combustion engine rises and lessens fuel economy.
When there is used the conventional injector which is equipped with an injection port having multiple holes, on the other hand, the atomization of the fuel spray is achieved by thinning each of the stream lines which are injected from the individual ports of the injection port. If these thinned stream lines interfere, however, the fuel particles will again grow larger. With the grown large particle diameter of this case, the effect to atomize the fuel spray drops. In order to avoid this grow of the fuel particles, therefore, it is necessary to widen the spray angle of the injector. With this enlarged spray angle, however, the fuel spray is liable to impinge to wet intake port wall parts, thereby causing a problem that the port wetting amount increases.